The present invention relates to global location registers in cellular networks and, more particularly, but not exclusively to methods and apparatus for improving their integration into the cellular network in which they are being used.
The global location register has two principle uses, firstly there is the originally intended use of reducing the level of international signaling by obviating the need to send an update location signal to a home location register every time a roaming user moves from one visitor location register to another. The second use is to reduce the opportunities for the home network to redirect the roaming user to some other preferred network.
The operation of the global location register and its context in the light of the above two uses is now explained.
The global location register, or GLR, is a node which is positioned between the VLR and/or Serving GPRS Support Node (SGSN—responsible for the delivery of data packets from and to the mobile stations within a geographical service area.) and the HLR. The GLR optimizes the location updating and the handling of subscriber profile data across network boundaries. When a subscriber roams, the GLR emulates the VLR and SGSN for the HLR in the home network. The GLR thus relays all traffic between the HLR and VLR or SGSN, keeping track of the latest location of the roaming user in the process. The HLR only needs to know about the GLR and thus there is no need to tell the HLR about the latest VLR update locations of the roaming users as he moves around the network.
By handling most of the location procedures without involving the HPMN, the GLR happens to provide an anti-Traffic Redirection feature as well, in that without the update location messages the home network has no opportunity to operate its traffic redirection. The GLR is defined by the 3GPP standards, and is referenced by ETSI specifications 23.119, 29.119, 29.120.
Concerning traffic redirection, there are many mobile or cellular network operators, or providers, in the world, usually more than one in a single country. These network operators include, but are not limited to, operators who provide mobility services using GSM, GPRS, 3G, CDMA, TDMA, PHS, WCDMA, IDEN and WLL technologies or their variants. These network operators provide voice and data services to their own subscribers and to subscribers from other networks. When the network operator provides service to a subscriber from a foreign country, it is referred to as “international roaming”. When the network operator provides service to a subscriber from another network in the same country, it is referred to as “domestic roaming”.
A cellular network with which a cellular subscriber has a direct billing relationship is often referred to as the Home Public Mobile Network (HPMN) or as the home network of the subscriber. If the subscriber is in a network with which it does not have a direct billing relationship, the serving network is referred to as the Visited Public Mobile Network (VPMN) or as the visited network. The subscriber is referred to as an inbound roamer by the VPMN. The same subscriber is referred to as an outbound roamer by the HPMN. In such a case, the inbound roamers are treated as temporary subscribers from a service availability perspective, while the billing for usage incurred by them is through inter-carrier settlements via the home network of the subscriber.
In recent years, the revenues to network operators from home subscribers have consistently declined due to increased competition and resultant pricing pressures. On the other hand, revenues from roamers have consistently grown in the same period due to increased mobile penetration in local markets and an increase in travel. Moreover, roaming revenues are high-margin revenues that typically comprise between 8-25% of the total network operator revenues. Hence, protecting the existing roaming revenues and increasing them further has become an important priority for network operators worldwide.
VPMN operators, aware of the growing significance of inbound-roamer revenues for their profitability, do their best to protect and further increase their share of roaming revenues, gained from inbound-roaming in their service areas. An inbound roamer himself may also have his own preferences, based on attractive roaming rates, availability of services, etc.
HPMN operators have preferences with regards to different VPMNs to be used by their subscribers when roaming abroad. Many network operators have partnership agreements with each other that include more favorable roaming charges between then. Some operators also own or are business-grouped with networks in various countries. These operators would like to make sure their outbound-roamers stay within the group, or roam in preferred networks.
There are currently some products in the mobile cellular market which help HPMN operators redirect network selection of roaming mobile cellular phones.
Such products are offered, for example, by StarHome GmbH.
These products typically work in association with the HPMN (the home network) to issue various rejection messages in response to registration attempts of roamers trying to register to a VPMN which is not preferable as far as the operator of the HPMN is concerned. Such a rejection message causes the mobile unit/handset, which is generally kept in an automatic network selection mode, to search for another network. Networks selected by the handset may continue to be rejected by the HPMN using such rejection messages, until the handset eventually chooses the network preferred by the HPMN.
In GSM networks, the above products monitor the update location SS7/MAP messages that are sent by the mobile unit as registration messages to the VPMN and then on to the HPMN. Rejection may be by not replying at all, so that the request times out, or it may be by actually sending a rejection signal to the VPMN. The product may be based on a monitor or probe placed on the SS7/MAP signaling lines.
Alternative products send a list of available networks in order of preference to the individual handset. The list is typically provided by Over the Air SIM update and is combined with a SIM applet. The list is used by the handset to search for available VPMNs in order.
Roaming redirection to preferred networks is now discussed with reference to FIG. 1, which illustrates deployment of a prior art redirection unit. A redirection unit 120 may be deployed on the international SS7 signaling lines 115 in association with the home network (HPMN) 110 of mobile unit 140. The redirection unit may comprise a probe part 130. Alternatively as mentioned the redirection unit can be implemented as a relay, thus forming part of the signaling path itself.
The probe part 130 picks up passing signals to carry out detection of roaming activity by mobile units, such as unit 140, in a roaming environment 150, such as a foreign country to which home network 110 does not extend.
The home network 110 is the network which the roaming unit 140 is subscribed to. The roaming unit roams in a roaming environment 150, which includes a number of mobile networks, VPMN 1-3 in this example, which are technologically compatible with the roaming mobile unit 140 and which the roaming mobile unit 140 may use.
The home network 110 may have preferences over the VPMNs, for example, the home network 110 may prefer a network which belongs to the same parent company. Utilizing the redirection unit 120, the home network 110 may attempt to manipulate the mobile unit 140 into selecting a network which it regards as preferable.
The redirection unit 120 may send a manipulative output, through an output port 190. The manipulative output may include a rejection message sent in response to the detection of roaming activity in a non-preferred network, say VPMN 1 in the given example. The mobile unit attempts to register to non-preferred network VPMN 1, and the attempt is rejected. The mobile unit 140 now automatically searches for another network. It may find VPMN 1 again, or it may find VPMN 2 or VPMN 3. If it finds VPMN 1 or 3 it is rejected and continues searching. At some stage it finds VPMN 2. The selection is accepted and registration is completed.
Reference is now made to FIG. 2 which is a flow chart illustrating an exemplary redirection process, in a GSM environment, by the home network (HPMN), according to prior art.
When a visited network (VPMN) network communication base station receives a registration message—an update location (UL) MAP message from the mobile handset 210, trying to roam in the VPMN, the message is forwarded to a Visitors Location Register (VLR) 220, which is a local database maintained by the VPMN to track visiting mobile unit users while the users are roaming in the VPMN.
The HPMN receives the update location message 230, and would normally register the location of the mobile unit in an HLR—The main database of permanent subscriber information for the HPMN.
A responding rejection message is then sent 240 to the VLR in the VPMN from a Home Location Register (HLR) of the HPMN, or from a redirection system, emulating the HLR for this purpose, which is deployed in the HPMN.
The rejection message is forwarded to the mobile unit (MU) 250.
The mobile unit/handset (MU), which is typically in an automatic network selection mode, automatically issues a preset standard number of attempts to register for the visited network by repetitive sending of the UL message for the VPMN to the home network 260.
According to the GSM standard, a mobile unit is preconfigured to issue four such registration attempts, and then search for another network. The reason for this is that users have the facility to hand-pick the desired network. The standard requires providers to honor the handmade selections of the users.
The home network thus manipulatively rejects these UL messages, and the mobile unit is maneuvered to search for another VPMN network in this successful redirection 290. A second found VPMN, in its turn, may also be rejected by the HPMN, and so forth until a HPMN preferred network is finally found.
As mentioned above, handsets are provided with a mode in which the user is able to manually select a network. In this manual mode, the mobile unit/handset shows a list of available networks to the user. The user selects one of the available networks and the handset attempts registration onto that network. If the registration is not successful, the handset waits for a predetermined delay and tries again. According to the GSM standard, in non-manual modes the number of retries is limited to four, so that a fifth retry may be recognized as manual mode. However, if specific handsets are configured for a different number of retrials, say five, the HPMN system may be configured accordingly, say to six, for this type of handset. In manual mode, the user himself has selected a particular network, so preferred VPMN selection from the HPMN perspective should not apply and the HPMN deployed redirection unit is expected to honor the will of the handset user.
However, a majority of current handsets are kept in automatic selection mode as the manual mode is not known to most users, and the HPMN is keen on controlling or influencing the selection of a VPMN.
In any event, with the deployment of such network selection systems at the HPMN, both the operator of the VPMN and the roaming user are left dependent on the HPMN systems when trying to exercise fair competition and the freedom to choose among different networks.
Reference is now made to FIG. 3, which is a simplified block diagram illustrating a VPLMN 300 that is equipped with a Global Location Register GLR 310. VPLMN 300 has four VLRs 320.1 . . . 320.4, and ordinarily, each time a roaming unit moves from one VLR to the other an update location signal is sent to the HLR 330 of the respective roaming unit. The presence of the update location signal on the international signaling lines is an opportunity for redirection of the kind listed above. The GLR however acts as a proxy to the VLRs 320.1-320.4 for the benefit of the HLR 330 at HPLMN 340, so that the HLR sees only the GLR and the GLR actually keeps track of which mobile unit is actually at which VLR. The result is that update location messages, other than the first, do not need to cross the International signaling lines and thus the opportunity for manipulative redirection is lost.
The process is illustrated in FIG. 4. In stage 410, a registration message is issued by the mobile unit when moving between two VLRs within the visited network 300. The new location registration is recorded only by the GLR 310, in stage 420. The forwarding of this new information to the HPMN is blocked. Instead the only forwarding is that indicated in stage 430, of the initial registration to the network where the GLR is recorded at the HPMN as the current VLR. The HPMN registers only the GLR itself as a location of the roaming mobile unit, with the advantage of limiting the attempt at redirecting the selection of a visited network to the very initial stage when the unit originally registered in the visited network. The GLR is the only location that knows the actual VLR and it forwards messages to the correct VLR as appropriate.
In essence, the GLR hides the VLRs behind it so that an update location message does not need to be sent. The home network (HPLMN) takes the GLR as the current location, and sends everything there. The GLR keeps track of the actual current VLR and relays all messages thereto.
Operating a GLR is thus advantageous to reduce the opportunity for home networks to carry out roaming network selection against the interests of the current network. However the GLR also has a disadvantage in that any errors in the GLR can cause malfunctions that propagate over the entire network. Errors in the GLR are difficult to correct and also shutdown of the GLR in order to overcome errors is likely to introduce further errors since home networks do not know the actual VLR. They may thus lose track entirely of their roamers. Furthermore the GLR can introduce problems of its own. For example different VLRs are free to assign their own local identification numbers (LMSI numbers). There is no problem when two VLRs assign the same number since the different VLR address used as a prefix allows the two telephones to be distinguished. However, if a GLR is used then there is no different VLR address allowing a distinction to be made.
There is thus a need to overcome the above problems in order to make the GLR more usable.